import java.util.Scanner;

public class test {
    public static int fib(int n){
        if(n == 1){
            return  0;
        }
        if(n == 2){
            return 1;
        }
        return fib(n - 1) + fib(n - 2);
    }
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int i = scan.nextInt();
        System.out.println(fib(i));
    }
}
